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A model experiment with heavy metal-treated nutrient solution was completed to examine responses of lettuce (Lactuca sativa L. ev. Grand Rapids) to these heavy metals. The lettuce growth was sharply inhibited by respective treatments of Cd 1㎎/ℓ, Cu 5㎎/ℓ, Pb 10㎎/ℓ and Zn 10㎎/ℓ. The most severe symptom appearing chlorosis was shown at 1㎎/ℓ Cd supply while the critical levels of toxicitiy of Cu and Zn were more than 10㎎/ℓ concentration in nutrient medium. At 0.1㎎/ℓ Cd in the nutrient solution, Cd concentration in lettuce leaves was 1.19㎎/ℓ which represented no external symptoms and no growth retardation with time. Cd and Zn contents in lettuce increased as the Cd concentrations in the nutrient solutions were increased. The Zn/Cd ratio of unity was noted for the Cd 0.1∼1.0㎎/ℓ treatment. Concentrated treatments, e.g., Pb 5.0㎎/ℓ, Zn 5.0㎎/ℓ and Cu 5.0㎎/ℓ, resulted in a 35∼40% fresh weight reduction. Pb and Cu contents in lettuce leaves were a little affected by increasing Pb and Cu concentrations added to the nutrient solution. However, Zn content was directly propertional increased to adding Zn supply to nutrient medium.
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